Elkhead Reservoir installs exclusion nets to help save four species of endangered fish

Striking a balance between the local sport-fishing community and environmentalists

The Situation

Located in Elkhead State Park in Colorado, Elkhead Reservoir provides 900 acres of recreational opportunities for park visitors, including a sport fishery. Because the reservoir’s native fish aren’t attractive as sport fish, other more popular species—such as catfish, trout, northern pike, and smallmouth bass—have been dumped into Elkhead.

Although the well-stocked reservoir pleased the local fishing community, the non-native additions quickly caused problems for the greater Colorado River system. Several of these species were escaping from the reservoir into surrounding rivers and eating the native fish—four of which were already endangered.

By 2002, the native and non-native fishspecies balance had swung dramatically to a population of nearly two-thirds non-native fish. Computer modeling showed there would never be success in controlling the non-native population in the river until leakage from Elkhead Reservoir stopped.

Problems with poison

Colorado Division of Parks & Wildlife sought to reclaim Elkhead Reservoir and reset the sport fishery by adding in new, less threatening fish that would not be as harmful to the native fish. In theory, this would allow Elkhead to develop a replacement fishery that is environmentally sustainable yet still palatable for the public.

To accomplish this, Parks & Wildlife officials looked at introducing a chemical called rotenone to the reservoir. Rotenone interferes with the fishes' ability to obtain energy from oxygen, essentially eliminating the fish population in the lake.

The local fishing community objected to this strategy.

River District Deputy Chief Engineer Ray Tenney explained, “Fishery management is a challenge, especially with the public involved. We couldn’t just poison the reservoir because people can dump non-native species back into the water, and in five years we’d have the same problem. Fishery managers have to come up with a fishery mix that the public likes to catch while still reducing the bass and pike populations. It’s a compromise.”

"Fishery management is a challenge, especially when the public is involved"

Screening for a sollution

As an alternative to poisoning the reservoir’s fish population, Elkhead pursued the use of fish screens. By putting screens over the spillway, Elkhead could potentially prevent the escapement of non-native fishes from reservoirs into the river where they interact with the endangered fishes. However, many experts were skeptical about the effectiveness of the screens due to the size of the openings and impact on the safety of the dam.

Because screens are more industrial in their mode of operation than a net solution and also not as kind to the fish, Elkhead decided to invest in a barrier net. This could provide the Parks & Wildlife fishery managers time to restructure the sport fishery in the reservoir without having to keep the net in place forever.

Effortless installation

In 2015, Elkhead contacted Pacific Netting Products to begin work on the project.

“We put a lot of stock in PNP’s extensive track record and unique expertise,” Tenney explained. “The representative projects that PNP had in place were impressive and made our project look small in scale. PNP had experience that could translate to our own project, and we felt comfortable with their expertise.”

PNP’s design concept for Elkhead Reservoir included three major components: a barrier net system, a floating debris barrier located upstream from the barrier net, and an anchoring system to secure both the net barrier system and debris bloom in position. With help from biologists, ¼-inch openings were chosen for the net based on when and where the fish spawn in the reservoir.

The net installation process was quick and painless. Previously, Elkhead had added a row of micropyle anchors under the reservoir. PNP came out to map those anchors and ensure that they were not only in the right position for the barrier net but also that they were secure enough for continued use.
After PNP did a dive inspection to approve use of the underwater anchors, the company worked with engineers to establish an anchoring system on the shore. Once all the anchors were in place, PNP installed the net by stapling it to the bottom and stapling it to the shore.

Benefits of Dyneema® Fiber

Part of what makes PNP’s barrier net solutions so effective—and easy to install—is the unique fiber used in making them. PNP barrier nets are made using Dyneema®, the proprietary brand name of HMPE (high modulus polyethylene) fiber manufactured by DSM. An ultra-high molecular weight, low density, highly crystalline linear polyethylene fiber, nets made with Dyneema® are as strong as, or stronger, than steel wire while weighing 85% less.

The advantages of using nets made with Dyneema® include:
• Quicker and easier to implement
• Better for the environment, more politically attractive
• More cost-effective than poisoning, which requires replacement fish
• The same strength as equivalent sized steel wire rope at 1/7 the weight
• Highest strength with least amount of surface area
• Low adhesion of marine growth
• Excellent UV, abrasion, and fatigue resistance
• Does not decay or absorb water
• Presents an extremely smooth surface for fish and marine life
• Longer lasting with less upkeep; Elkhead net is projected to last 8 to 10 years

“The net is a vital action for the Upper Colorado River Endangered Fish Recovery Program because it will benefit downstream endangered fish by preventing the escapement of non-native fish"

Outcomes

Completed in less than two years from conception, Elkhead’s new barrier net was installed in the fall of 2016 so it was ready for spring runoff. This solution enabled Elkhead to protect the endangered fish population by preventing the escapement of non-native species without impacting the local economy or upsetting sport-fishing enthusiasts. Thanks to the efforts of Pacific Netting Products and DSM, the Colorado pikeminnow, razorback sucker, humpback chub, and bonytail are now protected from the impacts of non-native fish.

The United States Department of Interior Fish and Wildlife Service concluded, “The net is a vital action for the Upper Colorado River Endangered Fish Recovery Program because it will benefit downstream endangered fish by preventing the escapement of non-native fish…We applaud your dedication and fortitude in seeing this project to completion.”

Migration of non-native and invasive aquatic species is a global concern. Pacific Netting Products is an expert in building exclusion, guidance, and collection nets that help protect fish from mortality caused by dams and hydropower plants, energy and industrial facilities, or agricultural operations. With DSM Dyneema’s innovative fiber, these net installations can be engineered on a massive scale—one net can be over two and half miles long—while still being highly cost effective. The result casts a far wider net of possibilities for addressing current and future environmental protection challenges without negatively impacting economic growth.